1. Field of the Invention
The present invention generally relates to metallization structures for integrated circuits on a semiconductor chip. In particular, the invention relates to a programmable electrical fuse with hybrid metallization including a high conductivity interconnect portion abutting a refractory metal interconnect portion.
2. Description of Related Art
A fuse is an electrical structure that is normally conducting that with the application of a suitable electrical current is “blown” to form an open in the circuit. Programming refers to applying a current to intentionally blow a fuse and create an open circuit. In integrated circuitry memory devices, fuses can be used for activating redundancy in memory chips and for programming functions and codes in logic chips. Specifically, dynamic random access memory (DRAM) and static random access memory (SRAM) may employ fuses for such purposes.
Electrical fuses (e-fuses) can also be used to prevent decreased chip yield caused by random defects generated in the manufacturing process. Moreover, e-fuses provide for future customization of a standardized chip design. For example, e-fuses may provide for a variety of voltage options, packaging pin out options, or any other options desired by the manufacturer to be employed prior to the final processing. These customization possibilities make it easier to use one basic design for several different end products and help increase chip yield.
Some e-fuses take advantage of electromigration effects to blow and create the open circuit. For example, electromigration can be defined as the transport of material caused by the gradual movement of ions in a conductor due to the momentum transfer between conducting electrons and diffusing metal atoms. In e-fuses that take advantage of electromigration effect, such transport of material caused by the gradual movement of ions can produce voids which cause the e-fuse to blow and create the open circuit or an increase in resistance above a pre-set target.
However, in a typical e-fuse, electromigration may cause unpredictable voids; thus, potentially creating the open circuit in undesirable locations. Furthermore, typical e-fuse programming may require high programming currents and long programming times. Such programming currents and times may result in unpredictable void formation which may negatively affect other circuits adjacent to the e-fuse. Therefore, it may be desirable to program an e-fuse with lower programming currents and shorter programming times. In addition, predictable and repeatable void formation may also be preferred.